1. Field of the Invention
The invention relates to a diagnostic method for a particle filter which is arranged in the exhaust gas stream of an internal combustion engine, a particle concentration being sensed by a particle sensor which is connected downstream of the particle filter.
Furthermore, the invention relates to a diagnostic system for a particle filter which is arranged in the exhaust gas stream of an internal combustion engine. The diagnostic system has an engine controller for setting combustion-relevant engine parameters as a function of different operating modes and for outputting at least one filter fault message. Furthermore, it has a particle sensor which is connected downstream of the particle filter in order to sense a particle concentration.
Furthermore, the invention relates to a suitable use of the diagnostic system according to the invention.
2. Related Art
An internal combustion engine is preferably a diesel engine. As an alternative, the internal combustion engine can be a gasoline engine or a gas-operated internal combustion engine. The internal combustion engine is typically provided for driving a motor vehicle, such as a passenger car. As an alternative, the internal combustion engine can be provided for steady-state operation, for example in an installation. In particular, the particle filter is a soot filter for diesel soot, and the particle sensor is a soot sensor.
The current particulate matter discussion for keeping the air clean has led vehicle producers to provide soot particle filters, in vehicles operated by diesel engine. To this end, an on-board diagnosis of all the emissions-relevant components of the vehicle is required. Corresponding malfunctions are entered in a fault memory of the vehicle. The owner of the vehicle is optionally advised to have his vehicle checked or repaired in a repair shop.
A differential pressure measurement is known from the prior art for monitoring the correct function of a particle filter. However, particle sensors are also known which are connected behind the particle filter and output a measured value which corresponds to the particle concentration in the exhaust gas stream at that point.
The maximum permissible particle concentrations behind the particle filter which are usually prescribed by law are extremely low and require a considerable outlay on measuring technology. Thus highly accurate particle sensors are required for future diesel systems in order to adhere to the EURO 5 limit values of less than 5 mg/km which correspond approximately to a volume-related limit value of 2 mg/m3. Sensors of this type have to have a detection threshold value which lies in the range of the volume-related limit value. In particular, a high absolute accuracy is required. In order, in addition, to take a sensor-dependent zero point drift and cross sensitivity into consideration in terms of measuring technology, the currently available particle sensors would have to have a considerably lower detection threshold value, such as 0.5 mg/m3. However, particle sensors with a high measuring resolution of this type are very expensive.